Block copolymers of polycarbonates including segments of other polymers have been known, see for example, Goldberg, U.S. Pat. No. 3,030,335, Adelmann, et al., U.S. Pat. No. 4,252,922, and Behnke et al., U.S. Pat. No. 4,436,839 which disclose block copolymers of bisphenol-A carbonates including segments derived from polyalkylene glycols. In Schreckenberg et al., U.S. Pat. No. 4,217,437, the polyalkylene glycols are advantageously end-functionalized, e.g., with diphenol carbonates. Such block copolymers are useful per se as film formers and shaped articles because of toughness conferred on the polycarbonates by the segments of other polymers. The block copolymers can also be blended with polycarbonate resins, and a whole host of other thermoplastic addition and condensation polymers to provide thermoplastic addition and condensation polymers to provide thermoplastic molding compositions showing markedly improved resilience properties compared with the unblended resins.
A highly useful family of heat resistant thermoplastic polymers is comprised of polyetherimide resins made by reacting a bis ether anhydride and an aromatic diamine. See, for example, Heath and Wirth, U.S. Pat. No. 3,847,867, who discloses the reaction product of 2,2-bis[4-2,3-dicarboxyphenoxy phenyl]propane dianhydride (BPA-DA) and metaphenylene diamine. The linear polymer is terminated with amino groups, and has a very high molecular weight and high melting point (Tg, typically=216° C.). Such a material cannot be readily blended with aromatic polycarbonate, because mixtures with two Tg's are obtained, one for the polyetherimide resin, and one for the polycarbonate. Furthermore, because of the amino terminal groups, polyetherimides cannot be successfully used as blocks in copolymers with aromatic polycarbonate segments, as is done with polyethers.
U.S. Pat. No. 4,611,048 discloses a method for preparing low molecular weight polyetherimides which are end functionalized with hydroxyl groups. When such polyetherimides are reacted with a polyhydric phenol and a carbonate precursor, there is surprisingly obtained a block copolymer which exhibits only one glass transition temperature Tg. Such low molecular weight polyetherimide copolymers also exhibit a high intrinsic viscosity, making them useful as engineering thermoplastics, and they are surprisingly compatible with other resins making available a number of new molding compositions.
An interfacial process for making the aforementioned low molecular weight polyetherimide block copolycarbonate was disclosed in U.S. Pat. No. 4,657,977. This process disclosed the formulation and isolation of the polyetherimide oligomer prior to its copolymerization with polycarbonate. Several disadvantages are associated with this method including the excessive number of steps required to produce the block copolycarbonate as well as the excessive number of pieces of process equipment required to produce the same. Further, the interfacial process of making the block copolycarbonate is believed to cause uneven distribution of the blocks within the copolymer due to slow reaction rates and or different reactivities of the dihydroxy and the polyetherimide oligomer. Such uneven distribution required that the polyetherimide blocks be kept at a low molecular weight to promote randomness of the blocks within the copolycarbonate and to promote a single Tg or a one phase system of the resulting copolycarbonate. It would be advantageous to find a process that provided a copolycarbonate wherein the copolycarbonate had polyetherimide blocks with high molecular weight while maintaining a single phase for the resulting copolycarbonate.